X-ray imaging systems have become a valuable tool in medical applications such as for the diagnosis of many diseases. As standard screening for breast cancer mammography 2-dimensional (2D) x-ray images are commonly used that record the images on a photographic film. Since mammograms take only 2D images across the entire breast tissue superimposition may occur. Thus, lesions may be masked by the tissue above or underneath, or normal structures may mimic a lesion. Since the accuracy of 2D mammograms are limited, especially in dense breasts, the addition of functional information can improve diagnostic accuracy.
For functional information, Contrast Enhanced Spectral Mammography (CESM) can be provided, which is a special type of mammogram that is performed after injecting x-ray intravascular contrast such as iodine. CESM involves the acquisition of x-ray images using multiple-energy radiation sequences. That is to say a number of images of the same object are acquired that reveal the x-ray transmittance of the object, such as a patient's breast, for differing x-ray spectra. In dual energy imaging, two images of the same object are acquired sequentially under different x-ray beam conditions as follows: One image at a low energy (LE) level, which is similar to a conventional 2D-mammographic image, and a second image at a high energy (HE) level, which is used for optimally detecting the contrast agent to indicate vascular information from angiogenesis. The image data at the different energy levels may be used to obtain energy selective images or in order to get the material decomposition of the object of interest. Hence, the data processing methods that make use of dual energy data may also be referred to as decomposition technique to obtain material decomposition images. This method enhances the contrast between different tissues or materials and especially when contrast material is used. After acquiring two images at different x-ray energies, the LE image and HE image are combined or subtracted to generate a functional image, which cancels the image contrast of adipose and glandular breast tissues and at the same time highlights areas with increased blood supply. Since breast cancer typically has a larger blood supply than normal tissue, the highlighted areas on the material decomposition images may aid in detection, diagnosis and staging of breast lesions.
The contrast enhanced spectral mammography (CESM) for 2D functional information in material decomposition images using the dual energy technique requires additional radiation exposure compared to a known 2D mammogram. The dose for dual energy CESM can be up to 1.4 times the dose of a known 2D mammogram. If a radiologist wants to further benefit from 3D morphological information along with a 2D functional image, he can perform besides the dual energy CESM imaging a digital tomosynthesis acquisition. In digital breast tomosynthesis (DBT) the volume information of an object of interest is usually derived from a series of images at various angles, wherein each so-called projection image is taken at substantially lower x-ray dose than the known 2D mammogram. However, if digital tomosynthesis is implemented besides 2D CESM the total dose delivered to the object increases up to 2.2 to 2.4 times the 2D regular mammography dose. Since the relatively high radiation dose limits the implementation of such combo techniques, there is the need to provide an imaging technique that performs both tomosynthesis and 2D CESM for lower radiation doses.